1. Field of the Invention
The present invention relates to systems and techniques for sensing atmospheric pollutants. More specifically, the present invention relates to sources for use in systems for remotely sensing atmospheric pollutants.
2. Description of the Related Art
Automobile exhaust contributes significantly to atmospheric pollution. Accordingly, efforts to abate adverse environmental impact due to automobile exhaust require an understanding of the nature of the pollutants therein. Accordingly, systems have been developed to measure pollutants in automobile exhaust.
The most accurate readings are acquired when the vehicle is in operation. This requires that the exhaust be measured remotely. Conventional remote sensing systems utilize optical sensors positioned along a roadside. The sensors measure absorption in the exhaust of optical energy at different wavelengths. The energy is typically provided from a first source of ultraviolet radiation (UV) and a separate second source of infrared (IR) radiation. Unfortunately, these dual source systems do not provide a simultaneous UV and IR measurement capability. That is, each sensor sees a different portion of the exhaust plume. Hence, these systems can not generally correlate data to a single section of the exhaust plume.
The use of dual sources is also problematic in that two sensor heads are required. This presents calibration problems, requires considerable signal processing and is not as compact as a single sensor arrangement.
Thus, a need existed in the art for a system and technique for providing a single source of infrared and ultraviolet radiation for use with systems for remotely sensing atmospheric pollutants in automobile exhaust.
This need was addressed by U.S. Pat. No. 5,210,702, entitled APPARATUS FOR REMOTE ANALYSIS OF VEHICLE EMISSIONS, issued May 11, 1993 to Bishop et al., the teachings of which are incorporated herein by reference. This system purports to use a single source of UV and IR radiation to analyze exhaust plumes. However, no means is provided for suppressing the visible radiation so that it is not sensed by the ultraviolet detector.
Thus, a need remains in the art for a system and technique for providing a single source of infrared and ultraviolet radiation for use with systems for remotely sensing atmospheric pollutants in automobile exhaust with a UV detector which is protected from visible radiation.